Amplifier for buoyant cable antenna

ABSTRACT

An amplifier for use in a buoyant cable antenna operable to receive signals within a frequency band includes: a first amplifier operable to provide amplified signals based on the received signals; a bandpass filter arranged to pass filtered signals within a first portion of the frequency band, the filtered signals being based on the amplified signals; an attenuator arranged in parallel with said bandpass filter and operable to attenuate signals within a second portion of the frequency band, the attenuated signals being based on the amplified signals; and a second amplifier operable to provide an amplified output including first amplified signals within the first portion of the frequency band and to provide second amplified signals within the second portion of the frequency band. The first amplified signals have a first gain, the second amplified signals have a second gain, and the first gain is more than the second gain.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/551,649, filed Sep. 1, 2009 and published Mar. 3, 2011 asU.S. patent publication no. 2011-0051555, which claims priority to andthe benefit of U.S. provisional patent application Ser. No. 61/104,351,filed Oct. 10, 2008, the contents of which are hereby incorporatedherein in their entireties.

STATEMENT OF GOVERNMENTAL INTEREST

This invention was made with U.S. Government support under the Naval SeaSystems Command, contract number N00024-04-D-8601. The U.S. Governmenthas certain rights in the invention.

BACKGROUND

The present invention is drawn to an amplifier and a processing systemenabling a submersible vehicle to accurately determine its location.

Conventional methods employed by submersible vehicles to determine theirlocation when submerged are prone to inaccuracies or unreliable. Moreaccurate methods used when on the surface are not available whensubmerged below periscope depth.

One conventional method submersible vehicles use for determining theirlocation is with inertial guidance systems. Inertial guidance systemsoperate by monitoring acceleration and changes in rotational attributeslike pitch, roll and yaw. This data along with the submersible vehicle'sspeed is processed by a computer to determine the current position ofthe submersible vehicle. Unfortunately, inertial guidance systems sufferfrom accumulated error. Any errors in measurement of the rotationalattributes are accumulated. With enough error accumulation, the totalerror can become significant enough to cause safety issues as theoperators of the submersible vehicle think they are at a particularlocation, but are actually at a very different location.

Submersible vehicles have several other methods for navigation includingsonar, radar, radio and Global Positioning System (GPS). Each of thesemethods has limitations with respect to their use. Submersible vehiclesmay operate in stealth mode wherein active sonar and radar methods ofnavigation may not be used because such methods may enable outsideobservers to determine the location of the submersible vehicle.Submersible vehicles can determine their location with radio navigationand a GPS, however both of these methods require the submersible vehicleto operate at periscope depth and extend an antenna above the surface ofthe body of water.

FIG. 1A illustrates a conventional method in which a submersible vehicleis able to determine its location using a GPS.

FIG. 1A includes a submersible vehicle 100 under the sea surface 102within an undersea region 116. Submersible vehicle 100 includes aperiscope 104 and an antenna 106. A GPS satellite 108 provides a radiosignal 110, whereas a GPS satellite 112 provides a radio signal 114.

The majority of submersible vehicle 100 is located in undersea region116. Periscope 104 and antenna 106 extend above the upper region ofsubmersible vehicle 100. When submersible vehicle 100 is at periscopedepth, as illustrated in FIG. 1A, it is able to use periscope 104 byextending it above sea surface 102. Submersible vehicle 100 usesperiscope 104 to view objects located on or adjacent to sea surface 102.At periscope depth, submersible vehicle 100 is able to extend antenna106 above sea surface 102. When antenna 106 is extended above seasurface 102, antenna 106 is able to receive radio signal 110 and radiosignal 114. GPS satellite 108 and GPS satellite 112 are located in orbitabove the earth. Submersible vehicle 100 is able to process radio signal110, and radio signal 114 to determine its location.

FIG. 1B illustrates submersible vehicle 100 when it is below periscopedepth and is not able to determine its location using a GPS.

As illustrated in FIG. 1B, submersible vehicle 100 is fully submergedbeneath sea surface 102. Antenna 106 is positioned beneath sea surface102 and is located in undersea region 116. Due to their highfrequencies, radio signal 110 and radio signal 114 are not able topenetrate into undersea region 116, where antenna 106 is located.Submersible vehicle 100 is not able to receive radio signal 110 andradio signal 114 and is not able to determine its location.

A conventional method for a submersible vehicle to determine itsposition, while below periscope depth, using GPS satellites will now bedescribed with reference to FIG. 2.

FIG. 2 illustrates a conventional method for a submersible vehicle todetermine its location using a GPS and a buoyant cable antenna (BCA).

FIG. 2 includes submersible vehicle 100 under the sea surface 102 withinan undersea region 116. Submersible vehicle 100 includes has a BCA 202attached thereto. BCA 202 includes a buoyant transmission cable portion204 and an inline amplifier 206, and a buoyant antenna portion 203. GPSsatellite 108 provides radio signal 110, whereas GPS satellite 112provides radio signal 114.

As illustrated in FIG. 2, submersible vehicle 100 is fully submergedwith antenna 106 and periscope 104 located in undersea region 116. Asdescribed previously and illustrated in FIG. 1B, antenna 106 is not ableto receive GPS radio signals 110 and 114. As a result, submersiblevehicle 100 is unable to determine is location with a GPS using antenna106.

However, the buoyant antenna portion 203 of BCA 202 floats on seasurface 102 while the other end is connected to submersible vehicle 100.Since buoyant antenna portion 203 floats on top of sea surface 102, itis able to receive radio signal 110 and radio signal 114. Radio signal110 and radio signal 114 would be conveyed from BCA 202 to submersiblevehicle 100. Inline amplifier 206 would be required to amplify radiosignal 110 and radio signal 114 to account for losses while travelingalong buoyant transmission cable portion 204. Submersible vehicle 100receives the amplified version of radio signal 110 and radio signal 114.Submersible vehicle 100 uses the amplified version of radio signal 110and radio signal 114 to determine its location with a GPS. However twoproblems still exist with this method.

The above described method determines the location of buoyant antennaportion 203. Only an approximate location of submersible vehicle 100 isdetermined as a result of the distance between an end of BCA 202 andsubmersible vehicle 100 as denoted by a separation distance 210.

A second problem with the above method is that conventional inlineamplifier 206 is not capable of providing sufficient amplification ofradio signal 110 and radio signal 114 to reach the interior ofsubmersible vehicle 100 with sufficient strength to be used to determinea position.

An example conventional inline amplifier 206 will now be described withreference to FIG. 3.

As illustrated in FIG. 3, inline amplifier 206 includes a filter 300, anamplifier 302, a gain compensation filter 304, an amplifier 306 and afilter 308.

Filter 300 is arranged to receive an input signal 310 and output afiltered signal 312. Amplifier 302 is arranged to receive filteredsignal 312 and output an amplified signal 314. Gain compensation filter304 is arranged to receive amplified signal 314 and output a compensatedsignal 316. Amplifier 306 is arranged to receive compensated signal 316and output an amplified signal 318. Filter 308 is arranged to receiveamplified signal 318 and output an output signal 320.

In operation, the end of BCA 202 receives a signal, for example from GPSsatellite 108. The signal is transmitted along buoyant transmissioncable portion 204 until it is amplified by inline amplifier 206.Specifically, filter 300 receives input signal 310 and passes a portionof input signal 310 that is within a predetermined frequency band(s) ofinterest and attenuates the remaining portions of input signal 310.

Amplifier 302 amplifies filtered signal 312.

Gain compensation filter 304 compensates for the signal attenuationcharacteristics of the transmission cable connected between output ofinline amplifier 206 and submersible vehicle 200. Specifically, gaincompensation filter 304 has a transfer function that provides anincremental increase in amplification for a predetermined portion ofamplified signal 314.

Amplifier 306 amplifies compensated signal 316.

Filter 308 receives passes a portion of amplified signal 318 that iswithin a predetermined frequency band(s) of interest and attenuates theremaining portions of amplified signal 318.

As discussed above, even if BCA 202 is able to transmit received GPSsignals to submersible vehicle 100, submersible vehicle 100 may notaccurately determine its location as a result of the unknown position ofbuoyant antenna portion 203 relative to submersible vehicle 100.

What is needed is a system and method for a submersible vehicle toaccurately determine its location when submerged.

BRIEF SUMMARY

It is an object of the present invention to provide a system and methodfor a submersible vehicle to accurately determine its location whensubmerged.

An aspect of the present invention is drawn to method of determining alocation of a submersible vehicle. The method includes obtaining firstbearing information based on a location of a ship at a first timerelative to the submersible vehicle and receiving broadcast informationfrom the ship, wherein the broadcast information includes locationinformation related to a second location of the ship at a second time, avelocity of the ship at the second time and a course of the ship at thesecond time. The method further includes obtaining second bearinginformation based on the second location of the ship at the second timerelative to the submersible vehicle, obtaining a velocity of thesubmersible vehicle at the second time and obtaining a course of thesubmersible vehicle at the second time. The method still furtherincludes determining the location of the submersible vehicle based onthe first bearing information, the second location of the ship at thesecond time, the velocity of the ship at the second time, the course ofthe ship at the second time, the second bearing information, thevelocity of the submersible vehicle at the second time and the course ofthe submersible vehicle at the second time.

Another aspect of the present invention is drawn to another method ofdetermining a location of a submersible vehicle. The method includesreceiving first broadcast information from a first ship, wherein thefirst broadcast information includes first location information relatedto a location of the first ship. The method additionally includesreceiving second broadcast information from a second ship, wherein thesecond broadcast information includes second location informationrelated to a location of the second ship. Further, the method includesobtaining first bearing information based on the location of the firstship relative to the submersible vehicle and obtaining second bearinginformation based on the location of the second ship relative to thesubmersible vehicle. Still further, the method includes determining thelocation of the submersible vehicle based on the first broadcastinformation, the second broadcast information, the first bearinginformation and the second bearing information.

Yet another aspect of the present invention is drawn to an amplifier foruse in a buoyant cable antenna operable to receive signals within afrequency band. The amplifier includes a first amplifier, a bandpassfilter, an attenuator and a second amplifier. The first amplifier canprovide amplified signals based on the received signals. The bandpassfilter is arranged to pass filtered signals within a first portion ofthe frequency band, wherein the filtered signals are based on theamplified signals. The attenuator is arranged in parallel with thebandpass filter and is operable to attenuate signals within a secondportion of the frequency band, wherein the attenuated signals are basedon the amplified signals. The second amplifier can provide an amplifiedoutput including first amplified signals within the first portion of thefrequency band and can second amplified signals within the secondportion of the frequency band. The first amplified signals have a firstgain, whereas the second amplified signals have a second gain. The firstgain is more than the second gain.

Additional objects, advantages and novel features of the invention areset forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF SUMMARY OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate an exemplary embodiment of the presentinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings:

FIG. 1A illustrates a conventional method in which a submersible vehicleis able to determine its location using a GPS;

FIG. 1B illustrates when a submersible vehicle is below a periscopedepth and is not able to determine its location using a GPS;

FIG. 2 illustrates a conventional method for a submersible vehicle todetermine its location using a GPS and a BCA;

FIG. 3 illustrates an example conventional inline amplifier within aBCA;

FIG. 4 illustrates a submerged submersible vehicle that is able toaccurately determine its location in accordance with an aspect of thepresent invention;

FIG. 5 is an overhead view of an area having a submerged submersiblevehicle and two ships;

FIG. 6 illustrates example relative positions of a submerged submersiblevehicle and a ship.

FIG. 7 is a flow chart describing an example method of determining asubmerged submersible vehicle's location in accordance with aspects ofthe present invention;

FIG. 8A is a graph of the AIS frequency band;

FIG. 8B is a graph of the band of signals that are receivable on BCAused by a submersible vehicle;

FIG. 8C is a graph of the band of signals that are receivable on a BCAused by a submersible vehicle after having been amplified with an inlineamplifier having the transfer function of FIG. 10;

FIG. 9 illustrates an example inline amplifier in accordance with anaspect of the present invention; and

FIG. 10 is a transfer function of an example inline amplifier inaccordance with an aspect of the present invention.

DETAILED DESCRIPTION

The International Maritime Organization (IMO) requires designatedcommercial (and other) vessels to carry and use Automatic IdentificationSystem (AIS) transponder/receiver sets to broadcast critical own-shipdata for the purpose of providing safety of ship situational awarenessto all vessels transiting in a given area. For example, vessels carryinga Class A AIS unit broadcast the following information every 2 to 10seconds while underway (less often while at anchor): a unique MMSI IDnumber, navigation status, latitude and longitude coordinates (to1/10000 minute), position accuracy, rate of turn, course and speed overground, true heading, and UTC time stamp. More descriptive ship data(e.g., vessel call sign, cargo, ship type, etc.) is transmitted every 6minutes. Vessels in the area equipped with AIS hardware can receive thisdata, transmitted at a frequency of approximately 162 MHz, from otherships in their area and display it on an electronic geographic displayor Geographic Information System (GIS) display that resembles a “bird'seye view” radar plot.

In accordance with an aspect of the present invention, a submergedsubmersible vehicle can access AIS data transmitted by vessels in thearea by any known manner, non-limiting examples of which include by wayof a buoy or BCA. The submerged submersible vehicle will effectivelyhave access to an “artificial” constellation of GPS “satellites” sincethe exact GPS position of each vessel (or “satellite”) is known withcertainty.

The submerged submersible vehicle may then determine the bearing of eachvessel by any known manner, a non-limiting example of which includessonar. For example, assuming the submerged submersible vehicle's sonaroperators can correlate these vessels with a specific sonar contact, forexample by using standard submersible vehicle sonar classificationtechniques, the bearing to each vessel can be determined. If bearings ofat least two correlated sonar contacts are available, the calculatedgeodetic position, which is based on the bearings to the vessels andtheir geodetic position, and which is where the sonar bearings cross, isthe submerged submersible vehicle's real-time position. If AISinformation for only one vessel is known and that information can becorrelated to real-time sonar bearings, it is possible to use standardsubmersible vehicle target motion analysis (TMA) equations andtechniques, along with own-ship speed and course data, to calculate thesubmerged submersible vehicle's position.

The benefit of the system and method of the present invention overconventional position fix taking techniques discussed above withreference to FIGS. 1A-2 is that the calculated position for thesubmerged submersible vehicle is independent of the position of thesensor used to collect the AIS information, and is available whilesubmerged. Moreover, the submerged submersible vehicle can continue tocalculate GPS-level fix positions for itself as long as the submersiblevehicle receives valid AIS data from vessels in the area and the sonarbearings to those vessels are known.

Conventional submersible vehicle antenna/amplifier subsystems are notcapable of conveying received AIS signals to a submersible vehicle in amanner in which the receiving equipment can process it correctly. Inaccordance with another aspect of the present invention, an inlineamplifier increases the amplification of the frequency band for AISwhile retaining the conventional gain of all other frequency bands thatare not AIS.

Example embodiments of an aspect of the present invention will now bedescribed with reference to FIGS. 4-7.

FIG. 4 illustrates a submerged submersible vehicle that is able toaccurately determine its location in accordance with an aspect of thepresent invention.

As illustrated in FIG. 4: submerged submersible vehicle 400 is under seasurface 102; a ship 402 and a ship 404 are at sea surface 102; and GPSsatellite 108 and GPS satellite 112 are in orbit above ship 402 and ship404. Submerged submersible vehicle 400 includes a BCA 408, a processingsystem 406 and a sonar system 409. BCA 408 includes a transmission cableportion 204 and an inline amplifier 410. Ship 402 includes an antenna412 and an antenna 414, whereas ship 404 includes an antenna 416 and anantenna 418.

GPS satellite 108 transmits radio signal 424. GPS satellite 112transmits radio signal 420.

Ship 402 receives radio signal 424 and radio signal 420 via antenna 412.Ship 402 is then able to determine its position on Earth by standard GPStechniques. This process occurs approximately once per second, so Ship402 constantly knows its real-time geodetic position. ship 402broadcasts its position, velocity and course information formatted forAIS via radio signal 428 through antenna 414, every 2-10 seconds asscheduled by AIS network.

Ship 404 receives radio signal 424 and radio signal 420 via antenna 416.Ship 404 is then able to determine its position on Earth by standard GPStechniques Ship 404 broadcasts its position, course and velocityinformation formatted for AIS via radio signal 430 through antenna 418every 2-10 seconds as scheduled by AIS network.

Ship 402 receives radio signal 430 formatted for AIS and is able todetermine the location, velocity and course of ship 404. Similarly, ship404 receives radio signal 428 formatted for AIS and is able to determinethe location, velocity and course of ship 402.

Sonar system 409 is operable to acoustically locate targets relative tosubmerged submersible vehicle 400. BCA 408 is operable to receive radiosignal 428 from ship 402 and to receive radio signal 430 from ship 404.Processing system 406 is operable to process information retrieved withsonar system 409, radio signal 428 and radio signal 430 to accuratelydetermine the location of submerged submersible vehicle 400, as will nowbe described in greater detail.

Noise from ship 402, such as produced by the engine and/or propeller,produces a sound wave 432. Using sonar system 409, submerged submersiblevehicle 400 detects the presence and bearing of ship 402 with sound wave432. Noise from ship 404, such as produced by the engine and/orpropeller, produces a sound wave 434. Using sonar system 409, submergedsubmersible vehicle 400 detects the presence and bearing of ship 404with sound wave 434.

Processing system 406 uses the bearing developed from the sonarinformation from sound wave 432 that was received by sonar system 409 inconjunction with position information of ship 402 received in the AISinformation in radio signal 428 that was received by BCA 408 todetermine a geodetic line of position of submerged submersible vehicle400. Processing system 406 uses the bearing developed from the sonarinformation from sound wave 434 that was received by sonar system 409,in conjunction with position information of ship 404 received in the AISinformation in radio signal 430, which was received by BCA 408, toadditionally determine a second geodetic line of position of submergedsubmersible vehicle 400.

Using the combined sonar and AIS information received and for ship 402and ship 404, submerged submersible vehicle 400 is able to accuratelydetermine its own location as the intersection of the two (or more)geodetic lines of position. In accordance with this aspect of thepresent invention, the distance between the end of BCA 408 and submergedsubmersible vehicle 400, as denoted by separation 436, is not adetracting factor as is the case in the conventional system discussedabove with respect to FIG. 2. In particular, in accordance with thisaspect of the present invention, the location of BCA 408 with respect tosubmerged submersible vehicle 400 is not a relevant factor because ithas no relation to the sonar information received by sonar system 409from sound wave 432 and from sound wave 434. Further, the location ofBCA 408 with respect to submerged submersible vehicle 400 is not arelevant factor because it does not affect reception of the AISinformation in radio signal 428 and the AIS information in radio signal430. The sonar information received from sound wave 432, the sonarinformation received from sound wave 434, the AIS information in radiosignal 428 and the AIS information in radio signal 430 will be the sameregardless of the location of BCA 408 with respect to submergedsubmersible vehicle 400.

FIG. 5 is an overhead view of an area having submerged submersiblevehicle 400, ship 402 and ship 404.

As described previously with respect to FIG. 4, submerged submersiblevehicle 400 is able to receive AIS information broadcast by ship 402 andship 404. Accordingly, submerged submersible vehicle 400 will knowlocation, course and velocity of each of ship 402 and ship 404. Usingthe sonar information for ship 402, submerged submersible vehicle 400 isable to determine a bearing 502 of ship 402 relative to submergedsubmersible vehicle 400. Using the sonar information for ship 402,submerged submersible vehicle 400 is able to determine a bearing 504 ofship 402 relative to submerged submersible vehicle 400. The location ofsubmerged submersible vehicle 400 is at a point 506, where bearing 502and bearing 504 intersect.

There may be situations in which a submerged submersible vehicle mayonly receive AIS information that is broadcast from a single ship. Insuch cases, the submerged submersible vehicle will be unable toaccurately determine its position using the example method discussedabove with reference to FIG. 5. Another example method for calculatingthe location of a submersible vehicle using the sonar and AISinformation from a single ship in accordance with an aspect of thepresent invention will now be described with reference to FIG. 6.

FIG. 6 illustrates example relative positions of a submerged submersiblevehicle and a ship.

As illustrated in the figure: point 602 represents the latitude andlongitude location of a ship at a first time T₁; point 606 representsthe latitude and longitude location of a submerged submersible vehicleat time T₁; point 612 represents the latitude and longitude location ofthe ship at a second time T₂; and point 616 represents the latitude andlongitude location of the submerged submersible vehicle at time T₂. Attime T₁, the ship at point 602 is separated from the submergedsubmersible vehicle at point 606 by a range R₁. At time T₂, the ship atpoint 612 is separated from the submerged submersible vehicle at point616 by a range R₂. At time T₁, the ship at point 602 is traveling at avelocity and course V_(ship1) indicated by arrow 604, whereas thesubmerged submersible vehicle at point 606 is traveling at a velocityand course V_(sub1) indicated by arrow 608. Similarly, at time T₂, theship at point 612 is traveling at a velocity and course V_(ship2)indicated by arrow 614, whereas the submerged submersible vehicle atpoint 616 is traveling at a velocity and course V_(sub2) indicated byarrow 618. Dotted line 610 represents the bearing B₁, measured indegrees, of the ship from the submerged submersible vehicle at time T₁,whereas dotted line 620 represents the bearing B₂ of the ship from thesubmerged submersible vehicle at time T₂.

The ship will broadcast its position, velocity and course in accordancewith AIS protocol. In accordance with an aspect of the presentinvention, the submersible vehicle will then know: point 602, i.e., thelatitude and longitude location of the ship at time T₁; point 612, i.e.,the latitude and longitude location of the ship at a second time T₂; thevelocity and course of the ship at T₁, i.e., V_(ship1) indicated byarrow 604; and the velocity and course of the ship at T₂, i.e.,V_(ship2) indicated by arrow 614. Further, by using a sonar system, thesubmersible vehicle may determine: the bearing B₁ of the ship from thesubmerged submersible vehicle at time T₁, i.e., dotted line 610; and thebearing B₂ of the ship from the submerged submersible vehicle at timeT₂, i.e., dotted line 620. In accordance with an aspect of the presentinvention, the submerged submersible vehicle may accurately determineits own location using the known parameters V_(ship1), V_(ship2), andlatitude and longitude location 612 of the ship at time T₂, and thedetermined parameters B₁ and B₂.

A change in the bearing ΔB is calculated as:ΔB=(B ₂ −B ₁)/(T ₂ −T ₁).  (2)

Range R₂ can be calculated as:R ₂ =kψ/ΔB,  (3)where k is a constant 1,934 when range R₂ is measured in yards and is aconstant 1 when range R₂ measured in nautical miles, and where ψ is therelative speed of the ship (in knots) as compared to the submergedsubmersible vehicle across bearing B₂. With reference to FIG. 6, thecomponent of V_(ship2) that is perpendicular to bearing B₂ is subtractedfrom the component of V_(sub2) that is perpendicular to bearing B₂ todetermine ψ.

Using B₂ and B₁ as determined at times T₂ and T₁, respectively, forexample as determined using a sonar system in accordance with thepresent invention, the submerged submersible vehicle may calculate thechange in the bearing AB using equation (2) above.

Then, using V_(ship2), as provided in the AIS information broadcast fromthe ship at time T₂, the submerged submersible vehicle may calculate thecomponent of V_(ship2) that is perpendicular to bearing B₂. Then, usingthe known velocity and course of the submersible vehicle V_(sub2), attime T₂, the submerged submersible vehicle may calculate the componentof V_(sub2) that is perpendicular to bearing B₂. At this point, thesubmerged submersible vehicle may determine ψ. The submerged submersiblevehicle may then calculate range R₂ using equation (3).

There may be instances where B₁ is very close to B₂, such as for exampleif the ship and the submerged submersible vehicle are traveling at thesame velocity and course perpendicular to bearing B₁ and B₂. In such acase, using equation (2), the change in bearing ΔB approaches or equalszero. In such a case, R₂ will approach infinity using equation (3). Toprevent such unusable data, the submerged submersible vehicle may alterits course such that it will not have the same velocity and courseperpendicular to bearing B₁ and B₂ as the ship. This will create achange in bearing ΔB that increases from zero, thus providing usabledata.

Location 612 of the ship at time T₂ is known by the submergedsubmersible vehicle from received AIS information; bearing B₂,represented by dashed arrow 620, has been determined by the submergedsubmersible vehicle using sonar; and range R₂ has been calculated by thesubmerged submersible vehicle using equation (3). The submergedsubmersible vehicle may then accurately determine its own location 616as a point at a distance R₂ in the direction reciprocal to B₂ (B₂±180°)from the geodetic location of the ship at time T₂ 612.

An example method for calculating the location of a submersible vehicleusing sonar and AIS information in accordance with an aspect of thepresent invention will now be described with reference to FIG. 7.

FIG. 7 is a flow chart describing an example method 700 of determining asubmerged submersible vehicle's location in accordance with aspects ofthe present invention.

As illustrated in the figure, method 700 starts (S702) and the submergedsubmersible vehicle receives AIS information from nearby ship(s) (S704).As discussed for example with reference to FIG. 4, BCA 408 receives AISinformation within radio signal 428 from ship 402 and radio signal 430from ship 404.

It is then determined whether AIS information was received from a singleship or multiple ships (S706).

In the case where AIS information is received from multiple ships, thenthe submerged submersible vehicle retrieves sonar information for eachship (S708). As discussed for example with reference to FIG. 4, sonarsystem 409 receives sound wave 432 from ship 402 and sound wave 434 fromship 404 and generates sonar information related ship 402 and ship 404,respectively.

At this point, submerged submersible vehicle associates the sonarinformation with the received AIS information (S710). As discussed forexample with reference to FIG. 4, the AIS information within radiosignal 428 includes the location, velocity and course of ship 402 andthe AIS information within radio signal 430 includes the location,velocity and course of ship 404. Processing system 406 compares thelocations and velocities of ship 402 and 404 to distinguish which ship(and therefore which location) is associated with which sonarinformation.

The submersible vehicle then determines the location of the ships usingthe AIS information (S712). As discussed for example with reference toFIG. 4, the AIS information within radio signal 428 includes thelocation ship 402 and the AIS information within radio signal 430includes the location ship 404. Having associated ship 402 with thesonar information of sound wave 432, processing system 406 can determinethe submersible vehicle's 400 geodetic line of position associated withship 402. Having associated ship 404 with the sonar information of soundwave 434, processing system 406 can determine the submersible vehicle's400 geodetic line of position associated with ship 404.

The submersible vehicle then determines the location of itself (S714).Referring to FIG. 5, location 506 of the submerged submersible vehicleis at the intersection of line of position 502 from ship 402 and line ofposition 504 from ship 404. Processing system 406 now knows: bearing 504from sonar information of sound wave 434; bearing 502 from sonarinformation of sound wave 432; the location of ship 402 from AISinformation of radio wave 428; the location of ship 404 from AISinformation of radio wave 430. Processing system 406 may then accuratelydetermine location 506 of the submerged submersible vehicle.

It is then determined whether processing system 406 is still operatingto determine the location of the submerged submersible vehicle (S716).If processing system 406 is not operating to determine the location ofthe submerged submersible vehicle, method 700 stops (S718). Ifprocessing system 406 is still operating to determine the location ofthe submerged submersible vehicle, then the submersible vehicle againreceives AIS information (S704).

Returning to the determination as to whether the AIS information isreceived from multiple ships (S706), in the case where AIS informationis received from a single ship, then the submerged submersible vehicleretrieves sonar information for the single ship (S720). As discussed forexample with reference to FIG. 6, sonar system 409 receives a sound wavefrom a ship and generates sonar information related to the ship toidentify bearing 610.

The AIS information is then associated with the determined bearing(S722). For example, processing system 406 may associate the location ofpoint 602 with determined bearing 610.

Then the submerged submersible vehicle retrieves new sonar informationand new AIS information for the single ship (S726). As discussed forexample with reference to FIG. 6, at time T₂, the ship has moved to asecond location at point 612, whereas the submerged submersible vehiclehas moved to a second location at point 616. At time T₂, sonar system409 receives a second sound wave from the ship and generates secondsonar information related to the ship to identify bearing 620.

The location information within the AIS information is then associatedwith the new determined bearing (S728). For example, processing system406 may associate the location of point 612 with determined bearing 620.

The new velocity, course and location of the ship is then determined(S730). The new velocity, course and location of the ship at point 612is known from the newly received AIS information.

The new velocity and course of the submerged submersible vehicle is thendetermined (S732). The new velocity and course of the submergedsubmersible vehicle at point 616 is known by the submerged submersiblevehicle.

The location of the submerged submersible vehicle is then determined(S734). As discussed above with reference to FIG. 6: location 612 of theship at time T₂ is known by the submerged submersible vehicle asdescribed in step S726; bearing B₂, represented by dashed arrow 620, hasbeen determined by the submerged submersible vehicle using sonar asdescribed in step S726; and range R₂ has been calculated by thesubmerged submersible vehicle using equation (3). The submergedsubmersible vehicle may then accurately determine its own location 616as a point at a distance R₂ in the direction reciprocal to B₂ (B₂±180°)from the geodetic location of the ship at time T₂ 612.

It is then determined whether processing system 406 is still operatingto determine the location of the submerged submersible vehicle (S716).If processing system 406 is not operating to determine the location ofthe submerged submersible vehicle, method 700 stops (S718). Ifprocessing system 406 is still operating to determine the location ofthe submerged submersible vehicle, then the submersible vehicle againreceives AIS information (S704).

In accordance with an aspect of the present invention, a submergedsubmersible vehicle is able to determine its own location based on AISinformation that is broadcast from a ship in conjunction with a bearingof the ship with reference to the submerged submersible vehicle. Assuch, the submerged submersible vehicle must be able to receive the AISinformation that is broadcast from the ship.

The amplification and filtering provided by BCA 202 employing theconventional inline amplifier 206 discussed above with reference to FIG.3, is not sufficient to overcome the losses of transmission cableportion 204 in order to enable received AIS signals to be processed bysubmersible vehicle 100. Submerged submersible vehicles use the BCA 202to receive broadband signals in the VLF through VHF bands. An amplifierthat amplifies only a band in the vicinity of AIS signals wouldeliminate the submersible vehicle's 100 ability to receive the otherrequired broadband signals. Addition of another gain stage toconventional inline amplifier 206 would saturate the receiving equipmentused for the other broadband signals. What is needed is an amplifierthat provides a certain amount of gain to broadband signals andincreased gain in a desired band (AIS in this embodiment). This will bediscussed in greater detail below with reference to FIGS. 8A and 8B.

FIG. 8A is a graph of the band of desired signals, including AIS,wherein the y-axis is amplitude of the signal and the x-axis is thefrequency of the signal.

As illustrated in the figure, desired RF band 800 is bounded by a lowerfrequency cutoff 802 and an upper frequency cutoff 804. RF band 800 isthe frequency content of the signals transmitted by desiredtransmitters, including AIS. Lower frequency cutoff 802 is located at156 MHz, whereas upper frequency cutoff 804 is located at 163 MHz.

FIG. 8B is a graph of the band of signals received in the submersiblevehicle via BCA 202, after having been amplified with the conventionalinline amplifier 206, and transmitted via the transmission line 204,wherein the y-axis is amplitude of the received signal and the x-axis isthe frequency of the received signal.

FIG. 8C is a graph of the band of signals that are receivable on a BCAused by a submersible vehicle after having been amplified with an inlineamplifier having the transfer function of FIG. 10.

As illustrated in the figures, some signals within a band 810 havelarger amplitudes than RF noise 808. Due to attenuation in thetransmission line 204 higher frequency signals, including the desiredband (AIS) are not above the RF noise. Accordingly, lower frequencysignals within band 810 may be differentiated from RF noise 808 and maybe processed. However, signals within desired RF band 800 are not aboveRF noise 808. Accordingly, signals within desired RF band 800 may not bedifferentiated from RF noise 808 and may not be processed.

RF noise is present at all frequencies and is amplified along withsignals of interest at those frequencies. Adding more amplification toinline amplifier 206, as discussed above with reference to FIG. 2, wouldamplify all noise in received signal 310. This would overdrive inlineamplifier 206 and overwhelm all signals of interest.

FIG. 9 illustrates an example inline amplifier 900 in accordance with anaspect of the present invention.

As illustrated in the figure, inline amplifier 900 includes an amplifier902, a bandpass filter 904, a broadband attenuator 906, a combiner 908,an amplifier 910, a gain compensation filter 912, an amplifier 914 and abias tee 916.

Amplifier 902 is arranged to receive input signal 310 and to output anamplified signal 918. Bandpass filter 904 is arranged to receiveamplified signal 918 and to output a filtered signal 920. Broadbandattenuator 906 is arranged to receive amplified signal 918 and to outputan attenuated signal 922. Combiner 908 is arranged to receive filteredsignal 920 and attenuated signal 922 and to output a combined signal924. Amplifier 910 is arranged to receive combined signal 924 and tooutput an amplified signal 926. Gain compensation filter 912 is arrangedto receive amplified signal 926 and to output a filtered signal 928.Amplifier 914 is arranged to receive filtered signal 928 and to outputan amplified signal 930. Bias tee 916 is arranged to receive amplifiedsignal 930 and to output an output signal 932.

Inline amplifier 900 provides amplification of signals within thedesired (AIS) band at greater amplification than other signals outsideof the desired band in order to be able to allow processing andreception of AIS signals and still provide the required amplification tothe other broadband signals. In operation, amplifier 902 amplifies inputsignal 310. In an example embodiment, amplifier 902 amplifies inputsignal 310 by 30 dB.

Bandpass filter 904 filters amplified signal 918 to pass only thosesignals within a band in the vicinity of AIS, approximately 156 MHz to163 MHz. Broadband attenuator 906 concurrently attenuates amplifiedsignal 918 to limit the amplified RF noise in the parts of the band thatdo not require the additional gain the desired band requires. In anexample embodiment, broadband attenuator 906 attenuates amplified signal918 by 33 dB.

Combiner 908 combines filtered signal 920 and attenuated signal 922.This provides a signal that is preferentially stronger in the band ofinterest (approximately 156-163 MHz) Amplifier 910 amplifies combinedsignal 924. In an example embodiment, amplifier 910 amplifies combinessignal by 30 dB.

Gain compensation filter 912 compensates for signal attenuationcharacteristics of the transmission cable connected between output ofinline amplifier 900 and the submersible vehicle. Gain compensationfilter 912 has a transfer function that provides an incremental increasein amplification for signals within a band of 2 MHz up through the AISband. This again limits the amplified RF noise in the (lower) parts ofthe band that do not require as much amplification to overcometransmission line losses.

Amplifier 914 amplifies filtered signal 928. In an example embodiment,amplifier 914 amplifies filtered signal 928 by 30 dB.

Bias tee 916 separates a DC bias 934 from the submersible vehicle fromamplified signal 930 and provides it to the amplifiers. The total signalon the transmission line carrying output signal 932 comprises thecombination of amplified signal 930 from inline amplifier 900 to thesubmersible vehicle 100 and a DC bias signal 934 from submersiblevehicle 100 to inline amplifier 900.

FIG. 10 is a transfer function (graph) of the amplification of signalsthat are receivable on BCA 202 used by submersible vehicle 100, afterhaving been amplified with inline amplifier 900 of FIG. 9, wherein they-axis is amplitude of the signal and the x-axis is the frequency of thesignal.

As illustrated in FIG. 10, frequency band 1004 includes frequency band800 (FIGS. 8A-8C) at preferentially higher gain. This enables thedesired (AIS) band to be above the RF noise 808, and AIS signals may beprocessed.

Aspects in accordance with the present invention enable a submergedsubmersible vehicle to accurately determine its location using sonar andAIS information. In accordance with one aspect of the present invention,AIS information broadcast by nearby ships is used by a submergedsubmersible vehicle to determine the location, velocity and course ofthe ships. In one embodiment, AIS information received from at least twoships is used in conjunction with sonar information related to the shipsto determine the submerged submersible vehicle's location. In anotherembodiment, AIS information and sonar information received from one shipat multiples times is used to determine the submerged submersiblevehicle's location.

In accordance with another aspect of the present invention, an inlineamplifier for use in a BCA enables a submersible vehicle to receive AISsignals broadcast from nearby ships. The amplification of the receivedsignals overcomes the attenuation caused by the transmission cableconnecting the amplifier to the submersible vehicle. The amplifierreceives AIS signals along with other signals and noise. The signalslocated in the AIS frequency band are amplified more than other signals,and noise outside the AIS frequency band is attenuated. The selectiveamplification of the AIS frequency band amplifies the signals to a levelat which they can be processed by AIS receiving equipment. The selectiveamplification of the AIS frequency band along with the lesseramplification of the other signals prevents the other signals from beingamplified too much and saturating the receiving equipment used forprocessing the other signals, and allows the required amplification ofall the signals by not overdriving the output stage of inline amplifier900.

The example embodiments discussed above use a sonar system to determinea bearing of a ship with reference to the submersible vehicle. However,in accordance with aspects of the present invention, any known method ofobtaining a bearing of a ship with reference to the submersible vehiclemay be used.

The example embodiments discussed above use a BCA to retrieve AISinformation to determine a ship's geodetic location. However, inaccordance with aspects of the present invention, any known method ofobtaining a geodetic location of a ship may be used.

The foregoing description of various preferred embodiments of theinvention have been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The exemplary embodiments, as described above, were chosen anddescribed in order to best explain the principles of the invention andits practical application to thereby enable others skilled in the art tobest utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto.

What is claimed is:
 1. An amplifier for use in a buoyant cable antennaoperable to receive signals within a frequency band, said amplifiercomprising: a first amplifier operable to provide amplified signalsbased on the received signals; a bandpass filter arranged to passfiltered signals within a first portion of the frequency band, thefiltered signals being based on the amplified signals; an attenuatorarranged in parallel with said bandpass filter and operable to attenuatesignals within a second portion of the frequency band, the attenuatedsignals being based on the amplified signals; and a second amplifieroperable to provide an amplified output including first amplifiedsignals within the first portion of the frequency band and to providesecond amplified signals within the second portion of the frequencyband, wherein the first amplified signals have a first gain, wherein thesecond amplified signals have a second gain, and wherein the first gainis more than the second gain.
 2. The amplifier of claim 1, furthercomprising: a combiner arranged to receive the filtered signals and theattenuated signals and to output combined signals, wherein said firstamplifier is arranged to receive the received signals, wherein saidbandpass filter is arranged to receive the amplified signals, whereinsaid attenuator is arranged to receive the amplified signals, andwherein said second amplifier is arranged to receive the combinedsignals.
 3. The amplifier of claim 2, further comprising a gaincompensation filter arranged to receive the amplified output andoperable to output a compensated signal.
 4. The amplifier of claim 3,further comprising a third amplifier arranged to receive the compensatedsignal and to output a second amplified output.
 5. The amplifier ofclaim 4, wherein said attenuator is operable to attenuate the amplifiedsignals by 33 dB.
 6. The amplifier of claim 5, wherein said firstamplifier is operable to amplify the received signals by 30 dB, andwherein said second amplifier is operable to amplify the combinedsignals by 30 dB.
 7. The amplifier of claim 6, wherein said bandpassfilter is operable to pass filtered signals within the frequency bandthat is greater than or equal to 156 MHz and that is less than or equalto 163 MHz.